We study symmetry-breaking inflation within the framework of metric-affine gravity. By introducing a non-minimal coupling, $\beta(\phi)\tilde{\cal R}$, between the Holst invariant and the inflaton, both small-field and large-field inflationary predictions can be brought into agreement with the latest observational constraints. Remarkably, even for sub-Planckian vacuum expectation values,...
Currently, the search for primordial gravitational waves is largely focused on detecting the parity-odd polarization pattern in the Cosmic Microwave Background—the B-modes. Accurately interpreting B-mode measurements depends heavily on understanding their production mechanisms. A particularly compelling scenario involves gravitational wave generation through the interaction of axion with gauge...
The Hubble Tension is the discrepancy between the measured value of the Hubble parameter $H_0$ and its $\Lambda$CDM model prediction using CMB data. New Early Dark Energy (NEDE) addresses this tension using a triggered phase transition in the dark sector. In this work we constrain the properties of NEDE using recent CMB and supernovae datasets, as well as the new BAO data from the DESI survey....
The Palatini formulation of gravity has been successfully used to motivate several observationally viable models of inflationary expansion. While the Palatini and metric formulations are equivalent in minimally coupled gravity, non-minimal scalar models are phenomenologically distinct depending on which formulation is used. At the same time, the recent hybrid approach to metric and Palatini...
In the phase space perspective, scalar field slow roll inflation is described by a heteroclinic orbit from a saddle type fixed point to a final attractive point. In many models the saddle point resides in the scalar field asymptotics, thus for a comprehensive view of the dynamics a global phase portrait is necessary. For this task in the literature one encounters dynamical variables that...
First-order phase transitions represent a golden opportunity into uncovering new physics as well as into the QCD phase diagram. These transitions typically proceed through nucleation, expansion and collision of bubbles. As a consequence, the spectrum depends on out-of-equilibrium properties that are challenging to obtain, such as the wall speed. In this talk I will review recent progress in...
Cosmological first-order phase transitions may have generated an observable gravitational wave background, offering a unique probe of beyond-Standard-Model physics. A crucial step in predicting this background is the reliable computation of bubble nucleation rates. In this talk, I will give an overview of recent advancements in perturbative high-temperature nucleation rate calculations. These...
The gravitational wave module in the Pencil Code is a versatile tool for computing the time-dependent three-dimensional strain field from a range of different sources in the early universe ranging from phase-transitional hydrodynamic and magnetohydrodynamic stresses to inflationary ones involving electromagnetic and axion pseudoscalar stresses. The solver utilizes the analytic solution for...
In the context of $f(R)$ gravity, as well as other extended theories of gravity, the correct counting of globally well-defined linear dynamical modes (i.e. gravitational-wave polarisations) has recently drawn a vivid interest. In this talk, we present a consistent approach shedding light on such issues for both so-called degenerate and non-degenerate $f(R)$ models embedded in Minkowski and de...
In this talk I will review the succesful search for Hellings-Downs correlations by the NANOGrav collaboration and the search for new physics with pulsar timing data. In particular, I will show the first model-independent search going beyond the simple power-law fit to characterise the frequency spectrum of the signal observed by the collaboration, allowing for a running of the spectral index....
Cosmological first-order phase transitions may have played a significant role in the formation of baryon asymmetry and dark matter, potentially leaving an observable gravitational wave signature. In this talk, I will focus on the possibility of primordial black hole formation from slow and strongly supercooled transitions. I will describe how the stochastic nature of the bubble nucleation...
The running-mass inflation model generates the primordial curvature perturbation spectrum that is consistent with observations at the pivot scale but exhibits a very large running at smaller scales. This creates favourable conditions for the formation of primordial black holes. In the current work we analyse a novel mechanism that provides the graceful exit for this model and enables us to...
We explore connections between two salient chaotic
features, namely Lyapunov exponent and butterfly velocity, for the class of asymptotically Lifshitz black hole background with arbitrary critical exponent by implementing three different holographic approaches, namely,
entanglement wedge method, out of time-ordered correlators (OTOC) and pole-skipping. We present a comparative study where...
Primordial black holes (PBHs), potentially formed in the early universe, may play a crucial role in cosmology, serving as seeds for supermassive black holes and contributing to the formation of merging black hole binaries observed by LIGO/VIRGO. They have also been proposed as candidates for dark matter. Another scenario involves cosmic strings, hypothetical linear defects predicted by various...
In the post-inflationary scenario, if PQ symmetry breaking occurs, a network of global cosmic strings are expected to form. At the time of the QCD phase transition, the previously scaling network of such defects will collapse by forming domain walls attached to strings. Given that all of the energy density of the string network is left behind into axion waves, in order to improve current...
The bulk action of the Yang-Mills theory based on the compact Lorentz group Spin(4)=SU(2)xSU(2) is determined by one parameter c_T. When c_T=1, the theory is right-handed and predicts a spin-2 field with the dynamics of the metric tensor in general relativity in the presence of dust. When c_T=0, the theory is achiral and has no local degrees of freedom. A transition from the latter to the...
